Over the last few years, the demand for high-speed communication networks has increased dramatically. In many situations, communication networks are implemented with electrical interconnections. That is the interconnections between nodes and networks are made using electronic circuitry such as a transistor switch which blocks or passes electrons. One type of electrical interconnection is an electronic network switch which is well known. The application of electronic network switches to local area networks (LANs), metropolitan area networks (MANs) and wide area networks (WANs) is also well know. A network switch may stand alone or be used in conjunction with or incorporated into other network equipment at a network node. As desired levels of bandwidth and transmission speed for communication networks increase, it will become more difficult for the electrical interconnections to satisfy these levels.
One difficulty associated with electrical interconnections is that they are sensitive to external electromagnetic interference. More specifically, electromagnetic fields that reside in the vicinity of the interconnection lines induce additional currents, which may cause erroneous signaling. This requires proper shielding, which hampered general heat removal.
Another difficulty is that electrical interconnections are subject to excessive inductive coupling, which is referred to as “crosstalk”. To alleviate crosstalk, the electrical interconnections must be shielded or abide by fundamental rules of circuit routing so that they are set at a distance large enough to prevent neighboring signals from having any adverse effect on each other, which would reduce network performance.
In lieu of electrical interconnections switching electrons or a voltage and current, optical interconnections offer a solution to the difficulties affecting conventional electrical interconnections. Optical interconnections switch photons or light ON and OFF at one or more wavelengths to provide signaling. An advantage to optical interconnections is that they are not as susceptible to inductive or even capacitive coupling effects as electrical interconnections. In addition, optical interconnections offer increased bandwidth and substantial avoidance of electromagnetic interference. This potential advantage of optics becomes more important as the transmission rates increase and as the strength of mutual coupling associated with electrical interconnections is proportional to the frequency of the signals propagating over these interconnections.
Albeit local or global in nature, many communications network features electronic switching devices to arbitrate the flow of information over the optical interconnections. Conventional electronic switching devices for optical signals are designed to include hybrid optical-electrical semiconductor circuits employing photodetectors, electrical switches, optical modulator or lasers. The incoming optical signals are converted to electrical signals by photodetectors. The electrical signals are amplified and switched by electronic switches to the appropriate output and then converted into optical signals by lasers. One disadvantage associated with a conventional electronic switching device is that it provides less than optimal effectiveness in supporting high data transmission rates and bandwidth.
An alternative approach is to develop an optical cross-connect system which performs switching operations of light pulses or photons (referred to generally as “light signals”) without converting and reconverting signals between the optical domain to the electrical domain. However, switching light or photonic signals is different and introduces additional challenges over conventional electrical switching. One of these challenges is fault protection. Failure modes in an optical system typically include a faulty component which can be catastrophic severing a communication channel or causing periodic generation of bit errors.
Another challenge to an optical cross-connect system, is generating status information regarding the data transmission status of the light or optical signals through the optical cross-connect. Yet another challenge in an optical cross-connect system is in creating a reliable optical cross-connect switch. Still yet another challenge in an optical cross-connect system is the ability to completely test such a system. These are challenges because the light or optical signals are not in an electrical form in an all optical cross-connect system and the data format and the data rate of individual channels is unknown to an all optical cross-connect system. Each and every channel can have their light pulses converted into electrical pulses for monitoring but this is an expensive solution which requires an optical to electrical conversion for each and every channel.